Abstract:

Effects of reaction conditions on the nitration of n-hexane with NO₂ were systematically studied, including reaction temperature, mole ratio of n-hexane to NO₂ and reaction time. The results showed that the conversion of n-hexane could reach 85.9% under the following reaction conditions: reaction temperature 120℃, mole ratio of n-hexane to NO₂ 1∶2 and reaction time 4h. Density functional theory (DFT) was used to study the reaction mechanism, the activation energies (E_a) of three possible reaction mechanisms were calculated at the B3LYP/6-311++G(3df,2pd)//B3LYP/6-31G* level. The calculated results are consistent with the experimental ones and further indicated that the crucial step of the process is the O atoms’ attacking of the H atoms, and 2-nitrohexane and 3-nitrohexane are the main products. The data of molecular geometry, atomic natural charge and IR spectra showed that the breaking of C—H bond and the formation of N—H are cooperative. Obvious changes of molecular geometry and atomic natural charge happened to the atoms of C(5), H(7), O(22), O(23) and N(21), which all participated in the nitration process.

Key words: alkane, nitrogen dioxide, nitration, computational chemistry, radical

摘要：

对NO₂硝化正己烷的反应进行了研究，分别考察了反应温度、摩尔比和反应时间的影响。结果表明：在反应温度为120℃、正己烷与NO₂摩尔比为1∶2、反应时间为4h的反应条件下，正己烷转化率可达85.9%。通过密度泛函理论（DFT）研究了NO₂硝化正己烷的反应机理，在B3LYP/6-311++G(3df,2pd)//B3LYP/6-31G*计算水平下精确计算了三个可能反应途径的活化能（E_a）。计算结果表明：该反应决速步骤为NO₂中O原子进攻正己烷中的H原子，其中2-硝基己烷和3-硝基己烷为主要产物，且计算结果与实验结果一致。分子几何结构、原子电荷和IR振动频率的数据表明C—H键的断裂和N—H键的形成是一个协同过程，参与硝化反应的原子C(5)、H(7)、O(22)、O(23)和N(21)的分子几何参数及其原子电荷有明显的变化。

关键词: 烷烃, 二氧化氮, 硝化反应, 计算化学, 自由基